Abstract
The application of dipolar proton (I) spin–lattice relaxation time measurements for the determination of fast quadrupolar spin–lattice relaxation rates on nonresonant S spins, the signals of which are too weak to be measured directly, are discussed in the limit of strong IS dipolar coupling. The spin–lattice relaxation of the common 1H–75As dipolar reservoir in KH2AsO4 and the common 1H–127I dipolar reservoir in Ag2H3IO6 are used to illustrate the above technique.